Texas Instruments TPS7A74EVM-068, Руководство пользователя, Страница: 6 / 19

The user has two options for providing a DC load on the output of the TPS7A74. J12 can be used to place a
DC load that flows through the current sense path on the output of the LDO. Alternatively, the J4 (VOUT) and
J18 (GND) banana connectors can be used for external measurements and loading; however, the IOUT loop
does not sense current flowing through these connectors. In cases where very fast transient tests are performed,
ringing may occur on VIN or VOUT as a result of the PCB parasitic inductance. Placing a strip of wire on the
exposed copper in the current path can reduce this ringing. 10 AWG wire can be used as needed. If ringing
persists, install damping networks by adding a series resistor and capacitor in parallel with VIN. Locations where
damping can be installed include C5 and R8, C6 and R9, C10 and R7, and C18 and R23.
WARNING
Current probe sensors can be tied to GND and must not come into contact with energized
conductors. See the user manual of your current probe for details. If your current probe has this
limitation, use a thin strip of electrical or Kapton
®
tape to isolate the current sense path from the
current probe.
Optional kelvin sense points are provided using the SMA connectors J1 (VIN) and J2 (VOUT).
2.4 Optional Load Transient Circuit Operation
The TPS7A74EVM-068 evaluation module contains an optional high-performance load transient circuit to allow
efficient testing of the TPS7A74 LDO load transient performance. To use the optional load transient circuit, install
the correct components in accordance with the application. Modify the input and output capacitance connected
to the TPS7A74 LDO to match the expected operating conditions. Determine the desired peak current to test,
and modify the parallel resistor combination of R12, R13, R14, R15, and R16 as shown:
I
Peak
=
VOUT
R12 R13 R14 R15 R16
(1)
The slew rate of the load step can be adjusted by C17, R17, R18, and R20. In this section, only R18 and R20
are adjusted to set the slew rate. For a 0-mA to 1.5-A to 0-mA load step, use
Table 2-1 to select a value of R18
and R20 that results in the desired rise or fall time.
Table 2-1. Suggested Ramp Rate Resistor Values
R18 R20 Rise, Fall Time
90.9 kΩ 97.6 kΩ 12 µs
44.2 kΩ 47.5 kΩ 6 µs
28 kΩ 23.2 kΩ 3 µs
14 kΩ 12.1 kΩ 1.5 µs
6.65 kΩ 5.9 kΩ 750 ns
3.24 kΩ 2.49 kΩ 300 ns
1.43 kΩ 1.21 kΩ 150 ns
Setup www.ti.com
6 TPS7A74EVM-068 Evaluation Module SBVU076 – APRIL 2022
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